The long term goal of this work is to elucidate the underlying molecular mechanisms leading to the development of neurofibrillary tangles(NFTs), a hallmark pathological feature of Alzheimer's disease.We will focus on the microtubule associated protein, tau, known to be the major molecular component of NFTs. Whereas normal tau is capable of interacting directly with microtubules and regulating their dynamics and stability, the abnormal tau found in NFTs is unable to bind microtubules concomitant with altered structural and functional properties. This project is designed to identify critical domains of tau and tubulin involved in the tau-tubulin interaction and possibly tau-tau interaction using the yeast two-hybrid system and a covalent cross- linking biochemical assay. The information obtained in these two assays will be used to perform X-ray crystallography studies of tau and tau-tubulin co-crystals (a join effort of the Feinstein and Kohlstaedt labs) by delimiting the important domains involved in the interactions. Understanding normal tau action provides an important foundation for the study of abnormal tau action in NFTs, a critical prerequisite for the development of rational therapies to address the problem of NFT formation.